1. The Field of the Invention
The present invention relates to a multi-piston variable capacity swash-plate type compressor of the type wherein the volume of a compressed refrigerant gas discharged from a discharge chamber is changed by varying tile angle of inclination of a swash-plate rotating in a crank chamber about an axis of rotation of a drive shaft through adjustably changing the pressure in the crank chamber, and more particularly, to a mechanical improvement to an internal capacity control means of a variable capacity swash-plate type compressor adapted for use in a refrigerating or an airconditioning system of an automobile.
2. Description of the Related Art
U.S. Pat. No. 3,861,829 granted to Robert et al discloses a typical variable capacity swash-plate type compressor suitable for being incorporated in an aircondditioning system of an automobile. The disclosed compressor of U.S. Pat. No. 3,861,829, is provided with a crank chamber in which a swash-plate mechanism for driving reciprocation of a plurality of compressor-pistons rotates with a drive shaft about an axis of rotation of the drive shaft, and the compressor-pistons reciprocating in respective compression chambers compress a refrigerant gas sucked into the compression chambers from a suction chamber and discharge the compressed gas from the compression chambers towards a discharge chamber. The discharge capacity of the compressor is varied by adjustably changing an angle of inclination of the swash-plate with respect to a plane perpendicular to the axis of rotation of the drive shaft to thereby change the reciprocating stroke of the compressor-pistons. The angle of inclination of the swash-plate is adjustably changed by controlling the pressure acting on the rear faces of the respective pistons with respective to the pressure in the suction chamber, and the control of the pressure differential between the pressure in the crank chamber supplied by blow-by gas from the compression chambers and that in the suction chamber is achieved by removing the blow-by gas from the crank chamber toward the suction gas circuit in the compressor in response to a detection of the abovementioned pressure differential.
Nevertheless, according to recent demand for a low-weight refrigerant compressor, the cylinder block and the pistons of a swash-plate type refrigerant compressor for an automobile refrigerating system are made of aluminum alloy. Further, the sealing between the pistons and the wall of the cylinder bores of the cylinder block is usually achieved by piston rings in the form of seamless rings made of synthetic material such as tetrafluoroethylene. The sealing property of the tetrafluoroethylene is, however, generally unstable, and therefore, the resin-piston rings deteriorate in time. Thus, during a long period of operation of the compressor, the amount of the blow-by gas flowing from the cylinder bores into the crank chamber tends to gradually increase due to deterioration of the sealing property of the resin-piston rings.
In order to eliminate the above-mentioned defect encountered by the conventional low-weight swash-plate type refrigerant compressor, Japanese Unexamined (Kokai) Patent Publication No. 1-142277 discloses an improved variable-capacity multi-piston type refrigerant compressor provided with a cylinder block having a plurality of cylinder bores, a suction chamber for refrigerant gas before compression, a discharge chamber for compressed refrigerant gas, a crank case having a crank chamber for receiving a rotatable swash-plate mechanism driving reciprocatory pistons in the cylinder bores, and a capacity control means having a supply means for stably supplying the crank chamber with a constant amount of high pressure gas to thereby accurately control the pressure in the crank chamber. Namely, the capacity control means of the compressor of Japanese Unexamined (Kokai) Patent Publication No. 1-142277 is provided with a through-hole means formed in the cylinder block so as to function as a throttle or choke arranged in a communicating passageway running from the discharge chamber toward the crank chamber. More specifically, the communicating passageway is formed as a stepwise through-bore piercing through the cylinder block and having a large diameter bore portion and a small diameter bore portion. The small diameter portion of the through-bore or a capillary tube fitted in the small diameter portion is used for constituting the throttle.
Nevertheless, the formation of the stepwise through-bore by the drilling method often results in residue of a certain amount of burr which is very difficult to remove. Moreover, since the formation of the through-bore having a diameter of, at most, 0.3 mm to 0.5 mm in the cylinder block made of aluminum alloy demands the use of a small diameter drill, a cutting chip of aluminum alloy in the form of a spiral sticks to the cutting edge of the drill. Accordingly, the accuracy of drilling of a small diameter through-bore is lowered and the production rate is also lowered.
Another proposal for improving the capacity control of a variable capacity swash-plate type refrigerant compressor has been known, in which a pin element having an orifice therein is arranged so as to project from a valve plate toward a discharge chamber in order to provide a throttle or choke in a communicating passage between the crank chamber and the discharge chamber. Nevertheless, the arrangement of the pin element projecting toward the discharge chamber brings about such a defect that since the flow rate of the compressed refrigerant gas starting from the discharge chamber and flowing through the primary refrigerating circuit is larger than that of the gas flowing from the discharge chamber into the crank chamber via the orifice of the pin element, a lubricant suspended in the refrigerant gas is carried by the compressed refrigerant gas flowing through the primary refrigerating circuit and accordingly, a sufficient amount of lubricant cannot be supplied into the crank chamber through the orifice of the pin element. Accordingly, the rotating elements of the rotating swash-plate mechanism in the crank chamber might not be adequately lubricated due to lack of lubricant.